The mechanisms that allow cells to sense and respond to [O2] are of fundamental importance in understanding a number of pathological processes. Recently the cellular [O2]-sensing mechanism has been identified as a family of [O2]-dependent prolyl hydroxylase enzymes (PHD). New studies by the PI have examined the consequences of activating the PHD oxygen-sensing pathway in cardiac myocytes using ethyl-3,4 dihydroxybenzoate (EDHB) and dimethyloxalylglycine (DMOG), small molecule agents that activate the PHD oxygen-sensing pathway. Activation of the PHD pathway is found to induce the levels of nitric oxide synthase-2 and heme oxygenase-1. Concurrent with these observed changes at the molecular level, a phenotype that is remarkably resistant to metabolic-inhibition (Ml) stress is conferred by the activation of the [O2]-sensing pathway in the cardiomyocyte. In particular, we find that mitochondrial function is protected during, and recovers better after Ml in cells where PHD pathway has been activated . The broad goals of the proposed work are to establish what changes occur as a result of the activation of the PHD-pathway, and to understand how these changes confer cardioprotection and influence the physiology of the heart cell. To these ends, a series of interrelated specific aims will be addressed. Specific Aim 1 will test if activation of the PHD pathway directs changes in cardiac cell physiology consistent with a hibernating phenotype and identify the energy consuming processes that are down regulated by the PHD-pathway. Specific Aim 2 is to determine how activation of the PHD-pathway protects the mitochondrion during a metabolic insult and promotes mitochondrial recovery upon washout of metabolic poisons or reoxygenation. Specific Aim 3 is to establish the HIF-dependence or-independence of PHD responses, and to identify novel non-HIF mediated actions of the PHD pathway. These studies will provide fundamental information regarding the specific molecular responses of the heart cell to hypoxic stress. The most direct applicability of these studies to human health lies in the fact that they will provide among the first characterization of the biological activity of a promising new class of drugs that can activate endogenous cellular protective mechanisms. These studies may lay the foundation for the development of Pharmaceuticals that induce protection against low oxygen levels or diseases involving poor blood flow.